runtime(java): Stop handpicking syntax groups for @javaTop (#14727)

* runtime(java): Stop handpicking syntax groups for @javaTop

Also:

- Remove the obsolete comment for g:java_allow_cpp_keywords.
- Remove the commented out groups java\%[Debug\]StringError.
- Infer and set the preferred formatting Vim options from
  the modeline.

Since vim-6-0u, non-contained syntax groups can be referred
to by using the "contains=TOP..." argument.

* Set &encoding and &termencoding to "utf-8" for test files

* Limit non-ASCII charset to [§ƒɐɘʬʭΑ-Τα-μ] for test files

Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/dumps/java_methods_indent8_03.dump

@@ -1,7 +1,7 @@
 | +0#00e0e07#ffffff0@7|@+0#e000e06&|T|ɐ|g@1|a|b|l|ɘ| +0#00e0e07&|@+0#e000e06&|T|ɐ|g@1|a|b|l|ɘ| +0#00e0e07&|a+0#4040ff13&|b|s|t|r|a|c|t| +0#00e0e07&|v+0#00e0003&|o|i|d| +0#00e0e07&|a|s|c|i@1|$|0|_|(|/+0#0000e05&@15| +0#0000000&@7
 | +0#00e0e07&@63|)|;+0#0000000&| @8
 | +0#00e0e07&@7|@+0#e000e06&|T|ɐ|g@1|a|b|l|ɘ| +0#00e0e07&|@+0#e000e06&|T|ɐ|g@1|a|b|l|ɘ| +0#00e0e07&|a+0#4040ff13&|b|s|t|r|a|c|t| +0#00e0e07&|<|α|,| |β|>| |Τ|ʬ|<|α|>| |μ|ʭ@1|$|0|_|(| +0#0000000&@17
-| +0#00e0e07&@23|/+0#0000e05&|*| |T+0#0000001#ffff4012|O|D|O|:+0#0000e05#ffffff0| |@|S|u|p@1|r|e|s@1|W|a|r|n|i|n|g|s|(|"|b|e|s|p|o|k|e|"|)|*|/| +0#00e0e07&|β| |𝛽|)|;+0#0000000&| @5
+| +0#00e0e07&@23|/+0#0000e05&|*| |T+0#0000001#ffff4012|O|D|O|:+0#0000e05#ffffff0| |@|S|u|p@1|r|e|s@1|W|a|r|n|i|n|g|s|(|"|b|e|s|p|o|k|e|"|)|*|/| +0#00e0e07&|β| |b|)|;+0#0000000&| @5
 @75
 | +0#00e0e07&@7>@+0#e000e06&|T|ɐ|g@1|a|b|l|ɘ| +0#00e0e07&|p+0#00e0003&|r|i|v|a|t|e| +0#00e0e07&|n+0#e000e06&|a|t|i|v|e| +0#00e0e07&|v+0#00e0003&|o|i|d| +0#00e0e07&|a|s|c|i@1|$|1|_|(|/+0#0000e05&|*|/@10|/+0#ffffff16#ff404010|*+0#0000e05#ffffff0|/|)+0#00e0e07&|;+0#0000000&| @9
 | +0#00e0e07&@7|@+0#e000e06&|T|ɐ|g@1|a|b|l|ɘ| +0#00e0e07&|p+0#00e0003&|r|i|v|a|t|e| +0#00e0e07&|n+0#e000e06&|a|t|i|v|e| +0#00e0e07&|<|α|,| |β|>| |Τ|ʬ|<|α|>|[|]| |μ|ʭ@1|$|1|_|(| +0#0000000&@19